U.S. patent number 10,121,753 [Application Number 15/642,810] was granted by the patent office on 2018-11-06 for enhanced solder pad.
This patent grant is currently assigned to Infineon Technologies AG. The grantee listed for this patent is Infineon Technologies AG. Invention is credited to Stefan Macheiner, Jens Oetjen.
United States Patent |
10,121,753 |
Oetjen , et al. |
November 6, 2018 |
Enhanced solder pad
Abstract
A solder pad includes a surface. A tin layer is arranged on the
surface. At least one out of a bismuth layer, an antimony layer and
a nickel layer is arranged on the tin layer.
Inventors: |
Oetjen; Jens
(Ottenhofen/Herdweg, DE), Macheiner; Stefan (Kissing,
DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG |
Neubiberg |
N/A |
DE |
|
|
Assignee: |
Infineon Technologies AG
(Neubiberg, DE)
|
Family
ID: |
60676346 |
Appl.
No.: |
15/642,810 |
Filed: |
July 6, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20180012854 A1 |
Jan 11, 2018 |
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Foreign Application Priority Data
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Jul 6, 2016 [DE] |
|
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10 2016 112 390 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
24/03 (20130101); H01L 21/4821 (20130101); H01L
24/05 (20130101); H01L 23/49582 (20130101); H01L
23/49527 (20130101); H01L 2224/32245 (20130101); H01L
2224/0346 (20130101); H01L 2224/48091 (20130101); H01L
24/73 (20130101); H01L 2224/0512 (20130101); H01L
2924/00014 (20130101); H01L 2224/73265 (20130101); H01L
24/48 (20130101); H01L 2224/0345 (20130101); H01L
2224/05023 (20130101); H01L 2224/05611 (20130101); H01L
2924/181 (20130101); H01L 2224/05568 (20130101); H01L
2224/48465 (20130101); H01L 2224/05113 (20130101); H01L
2224/48247 (20130101); H01L 2224/05573 (20130101); H01L
24/32 (20130101); H01L 2224/05155 (20130101); H01L
2924/181 (20130101); H01L 2924/00012 (20130101); H01L
2224/48091 (20130101); H01L 2924/00014 (20130101); H01L
2224/73265 (20130101); H01L 2224/32245 (20130101); H01L
2224/48247 (20130101); H01L 2924/00012 (20130101); H01L
2224/48465 (20130101); H01L 2224/48247 (20130101); H01L
2924/00012 (20130101); H01L 2924/00014 (20130101); H01L
2224/45099 (20130101) |
Current International
Class: |
H01L
23/00 (20060101); H01L 23/495 (20060101); H01L
21/48 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10 2010 028 199 |
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Oct 2011 |
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DE |
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10 2012 208 681 |
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Nov 2013 |
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DE |
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10 2014 217 923 |
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Mar 2016 |
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DE |
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1 245 328 |
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Oct 2002 |
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EP |
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2 768 293 |
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Aug 2014 |
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EP |
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101116283 |
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Apr 2011 |
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KR |
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00/48784 |
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Aug 2000 |
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WO |
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2005/099961 |
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Oct 2005 |
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WO |
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2006/114267 |
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Nov 2006 |
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WO |
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2007/070548 |
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Jun 2007 |
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WO |
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2009/117476 |
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Sep 2009 |
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WO |
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2015028813 |
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Mar 2015 |
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WO |
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2015/103362 |
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Jul 2015 |
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WO |
|
Primary Examiner: Stark; Jarrett J
Attorney, Agent or Firm: Dicke, Billig & Czaja, PLLC
Claims
What is claimed is:
1. A solder pad, comprising: a surface; a tin layer arranged on the
surface; and three layers: a bismuth layer and an antimony layer
and a nickel layer, which are arranged on the tin layer, wherein a
first of the three layers is arranged on the tin layer, a second of
the three layers is arranged on the first layer and the third of
the three layers is arranged on the second layer, wherein each
layer covers essentially the entire respective underlying
layer.
2. The solder pad of claim 1, wherein a thickness of the tin layer
lies in a range from about 5 micrometer to about 15 micrometer.
3. The solder pad of claim 1, wherein a thickness of the bismuth
layer lies in a range from about 2 micrometer to about 10
micrometer.
4. The solder pad of claim 1, wherein a thickness of the antimony
layer lies in a range from about 1 micrometer to about 6
micrometer.
5. The solder pad of claim 1, wherein a thickness of the nickel
layer lies in a range from about 0.1 micrometer to about 0.6
micrometer.
6. The solder pad of claim 1, wherein the tin layer, the bismuth
layer, the antimony layer and the nickel layer form a layer stack,
and wherein a plurality of such layer stacks are formed on each
other on the solder pad surface.
7. The solder pad of claim 6, wherein a total thickness of all tin
layer thicknesses in the plurality of layer stacks lies in a range
from about 5 micrometer to about 15 micrometer, a total thickness
of all bismuth layer thicknesses in the plurality of layer stacks
lies in a range from about 2 micrometer to about 10 micrometer, a
total thickness of all antimony layer thicknesses in the plurality
of layer stacks lies in a range from about 1 micrometer to about 6
micrometer, and a total thickness of all nickel layer thicknesses
in the plurality of layer stacks lies in a range from about 0.1
micrometer to about 0.6 micrometer.
8. The solder pad of claim 7, wherein all layers made of a same
material are of about the same thickness.
9. An electronic component, comprising the solder pad of claim
1.
10. The solder pad of claim 1, wherein the solder pad comprises
copper.
11. The solder pad of claim 1, wherein the solder pad comprises
aluminum.
12. The solder pad of claim 1, wherein the solder pad comprises a
copper alloy.
13. The solder pad of claim 1, wherein the solder pad comprises an
alloy 42.
14. The solder pad of claim 1, wherein the solder pad comprises a
steel alloy.
15. The solder pad of claim 1, wherein the solder pad comprises an
aluminum alloy.
16. The solder pad of claim 1, wherein the solder pad is plated
with a metal layer.
17. The solder pad of claim 16, wherein the metal layer comprises
silver.
18. A solder pad, comprising: a surface; a tin layer arranged on
the surface; and three layers: a bismuth layer and an antimony
layer and a nickel layer, which are arranged on the tin layer,
wherein the tin layer, the bismuth layer, the antimony layer and
the nickel layer form a layer stack, and wherein a plurality of
such layer stacks are formed on each other on the solder pad
surface.
19. A method for enhancing a solder pad surface of the solder pad
of claim 1, the method comprising: providing a solder pad
comprising at least one solder pad surface; plating or sputtering
tin onto the at least one solder pad surface to form a first tin
layer; plating or sputtering a first of three materials bismuth,
antimony, nickel onto the first tin layer to form a first material
layer; plating or sputtering a second of the three materials onto
the first material layer to form a second material layer; and
plating or sputtering the third of the three materials onto the
second material layer to form a third material layer.
20. The method of claim 19, further comprising: plating or
sputtering tin onto the third material layer to form a second tin
layer; plating or sputtering a first of three materials bismuth,
antimony, nickel onto the second tin layer to form a fourth
material layer; plating or sputtering a second of the three
materials onto the fourth material layer to form a fifth material
layer; and plating or sputtering the third of the three materials
onto the fifth material layer to form a sixth material layer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This Utility Patent Application claims priority to German Patent
Application No. 10 2016 112 390.0, filed Jul. 6, 2016, which is
incorporated herein by reference.
FIELD
The present disclosure relates in general to a solder pad. The
disclosure further relates to a leadframe. The disclosure further
relates to an electronic component, in particular an electronic
component including the solder pad. The disclosure further relates
to a method for enhancing a solder pad surface.
BACKGROUND
Electronic components may be mounted on a board to interact in an
electronic circuit. For example, the board may be a printed circuit
board (PCB). Fixing the electronic components to the board may be
effectuated by soldering the electronic components using solder
pads of the electronic components to solder pads arranged on the
board.
Board level reliability may be a challenge in high temperature
environments. Especially in automotive applications an improved
fixing of the components to the board may be demanding. In
automotive applications the board may be subject to a harsh
environment including high temperature and strong vibrations. A
connection quality of components to the board may be visible in the
temperature cycle on board (TCoB) performance.
A standard solder widely used in industry is an alloy including
tin, silver and copper. The alloy is known under the name SAC. The
alloy may be used in different compositions. One composition is
SnAg3.8Cu0.7. This alloy is known as SAC387. SAC387 may not meet
all requirements in a harsh environment. An actual SAC387 solder
performance may be inferior to a performance of tin-lead
solder.
SUMMARY
Various aspects pertain to a solder pad including a surface. A tin
layer is arranged on the surface. At least one out of a bismuth
layer, an antimony layer and a nickel layer is arranged on the tin
layer.
Various aspects pertain to a solder pad including a surface. A tin
layer is arranged on the surface. The tin layer includes particles
of at least one out of bismuth particles, antimony particles and
nickel particles.
Various aspects pertain to a method for enhancing a solder pad
surface. The method includes the following acts: providing a solder
pad including at least one solder pad surface; plating or
sputtering tin onto the at least one solder pad surface to form a
first tin layer; plating or sputtering bismuth onto the first tin
layer to form a first bismuth layer; plating or sputtering antimony
onto the first bismuth layer to form a first antimony layer;
plating or sputtering nickel onto the first antimony layer to form
a first nickel layer.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further
understanding of examples and are incorporated in and constitute a
part of this description. The drawings illustrate examples and
together with the description serve to explain principles of
examples. Other examples and many of the intended advantages of
examples will be readily appreciated as they become better
understood by reference to the following detailed description.
FIG. 1 schematically illustrates a first example of a solder pad in
accordance with the disclosure in a cross-sectional view.
FIG. 2 schematically illustrates a second example of a solder pad
in accordance with the disclosure in a cross-sectional view.
FIG. 3 schematically illustrates a third example of a solder pad in
accordance with the disclosure in a cross-sectional view.
FIG. 4 schematically illustrates a fourth example of a solder pad
in accordance with the disclosure in a cross-sectional view.
FIG. 5 schematically illustrates a fifth example of a solder pad in
accordance with the disclosure in a cross-sectional view.
FIG. 6 schematically illustrates a first example of an electronic
component in accordance with the disclosure in a cross-sectional
view.
FIG. 7 illustrates an example of a method in accordance with the
disclosure for enhancing a solder pad surface in a flow chart.
DETAILED DESCRIPTION
In the following description, examples are described with reference
to the drawings which form a part thereof wherein like reference
numerals are generally utilized to refer to like elements
throughout. In the following description, for purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of one or more aspects of
examples. However, it may be evident to a person skilled in the art
that one or more aspects of the examples may be practiced with a
lesser degree of these specific details. The following description
is therefore not to be taken in a limiting sense, and the scope of
protection is defined by the appended claims.
The various aspects summarized may be embodied in various forms.
The following description shows by way of illustration various
combinations and configurations in which the aspects may be
practiced. In this regard, directional terminology, such as e.g.
"upper", "lower", "top", "bottom", "left-hand", "right-hand",
"frontside", "backside", "vertical", "horizontal", etc., may be
used with reference to the orientation of the figures being
described. Since components of examples can be positioned in a
number of different orientations, the directional terminology is
used for purposes of illustration and is in no way limiting.
It is understood that the described aspects and/or examples are
merely examples and that other aspects and/or examples may be
utilized and structural and functional modifications may be made
without departing from the concept of the present disclosure. In
addition, while a particular feature or aspect of an example may be
disclosed with respect to only one of several implementations, such
feature or aspect may be combined with one or more other features
or aspects of the other implementations as it may be desired and
advantageous for any given or particular application.
Further, to the extent that the terms "include", "have", "with" or
other variants thereof are used in either the detailed description
or the claims, such terms are intended to be inclusive in a manner
similar to the term "comprise". Also, the term "exemplary" is
merely meant as an example, rather than the best or optimal.
Solder pads and methods for enhancing solder pads are described
herein. Comments made in connection with the described solder pads
may also hold true for corresponding methods and vice versa. For
example, if a specific material of a solder pad is described, a
corresponding method for enhancing a solder pad may include an act
of providing the corresponding material in a suitable manner, even
if such an act is not explicitly described or illustrated in the
figures. Similarly, the method may include an act of providing the
specific component.
Electronic components described herein may include one or more
semiconductor chips or semiconductor dies. The dies may be
manufactured by different technologies and may include, for
example, integrated electrical, electro-optical or
electro-mechanical circuits and/or passives. The dies may include
integrated circuits such as, e.g., logic integrated circuits,
control circuits, microprocessors, memory devices. The dies may be
of arbitrary type and need not be manufactured from specific
semiconductor material such as for example Si, SiC, SiGe, GaAs or
an organic semiconductor material, and, furthermore, may contain
inorganic and/or organic materials that are not semiconductors,
such as for example insulators, plastics or metals.
Solder pads and leadframes as described herein may be of different
materials. Examples of materials may include, but are not limited
to, copper, aluminum and silver-plated. A solder pad or a leadframe
may include copper, aluminum, a copper alloy, an alloy 42, a steel
alloy, an aluminum alloy and so on as a base material. The base
material may be plated with other metal layers.
Leadframes as described herein may include a die pad. A die pad may
have an upper surface and a lower surface opposite the upper
surface. A die pad may include a die mounting surface. The die
mounting surface may be on an upper surface. The die mounting
surface may be coplanar to the upper surface of the die pad. The
die mounting surface may be separated by the upper surface of the
die pad by a step, i.e. the die mounting surface may be in a
different plane than the upper surface. The die mounting surface
may be smaller than the die pad surface. The die mounting surface
may be arranged in the middle of the die pad.
Leadframes as described herein may include one or a plurality of
lead fingers. A lead finger may include an inner contact pad. In
one example, lead fingers may be arranged on one side of the die
pad. In a further example, lead fingers may be arranged all around
the die pad.
Solder pads as described herein may be of arbitrary form. For
example, a solder pad may have a flat surface. A solder pad in the
meaning of the present disclosure may also include convex or
concave surfaces. A solder pad may e.g. be formed by a surface of a
wire.
Solder pad surfaces as described herein may be covered by a tin
layer. An upper material layer may be provided on the tin layer.
During a soldering process the tin layer may interact together with
the upper material layer with a SAC solder, especially a SAC387
solder used for soldering the solder pad to a corresponding solder
pad.
During a soldering process an alloy may form in the vicinity of the
solder pad. The alloy may enhance stability of the formed solder
connection. In particular, the alloy may enhance stability of the
formed solder connection for higher operating temperatures. The
alloy may particularly enhance stability of the formed solder
connection for operating temperatures up to 150.degree. C. The
alloy may raise a creep resistance, thus increasing the durability
of the solder connection under temperature cycling conditions. A
melting temperature of the alloy may be in a same temperature range
as a melting temperature of the SAC solder used.
Solder pad surfaces as described herein may be covered by a tin
layer, and the tin layer may be covered by a bismuth layer, an
antimony layer and a nickel layer.
During a soldering process an alloy may form in the vicinity of the
solder pad based on the layer materials tin, bismuth, antimony and
nickel together with the materials included in the SAC solder, i.e.
tin, silver and copper. Tin may constitute the major part of the
alloy.
Bismuth and nickel may interact to form intermetallic phases NiBi
with 74 wt. % Bi or 91 wt. % Bi. The intermetallic NiBi phases may
harden the solder connection.
The alloy formed in the vicinity of the solder pad may include a
ratio of antimony to bismuth of about 1 to about 1.5 up to a ratio
of about 1 to about 3 (based on the antimony weight). This ratio
may lead to a low grain size structure in the solder
connection.
FIG. 1 shows in a cross-sectional view a solder pad 10. The solder
pad 10 may be of any form and size. In one example, a possible
solder pad size may be about 0.25 mm.quadrature.0.8 mm. In a
further example, a possible solder pad size may also be about 0.2
mm.quadrature.0.5 mm. However, a solder pad size may have any other
suitable dimension. The solder pad may be a flat pad integrated in
a housing of a so-called leadless package. The solder pad may be
part of a lead of a leaded package. The solder pad may be a wire.
It is to be noted that FIG. 1 is only intended to schematically
illustrate a cross-sectional view of a solder pad.
The solder pad 10 may include a surface 12. The surface of the
solder pad 10 may lie in a plane. The surface of the solder pad 10
may be of a convex form representing the surface of a wire. The
surface of the solder pad 10 may also have another suitable
form.
A tin layer may be arranged on the surface 12. The tin layer 14 may
have a thickness in a range from about 5 micrometer to about 15
micrometer. In an example, the thickness of the tin layer 14 may
lie in a range from about 7 micrometer to about 12 micrometer. In
another example, the thickness of the tin layer may lie in a range
from about 9 micrometer to about 11 micrometer.
A layer 16 may be disposed or arranged on top of the tin layer 14.
The layer 16 may be a bismuth layer, an antimony layer or a nickel
layer.
The solder pad 10 may be soldered with its surface 12, on which the
tin layer 14 and the further layer 16 are arranged, to a PCB using
an SAC solder paste. During the soldering process the tin layer 14
together with the upper layer 16 may interact with the solder
SAC387. The properties of the solder SAC387 may therefore be
modified in the vicinity of the solder pad 12. The bulk material
formed after board assembly may enhance the temperature cycle on
board performance.
FIG. 2 shows in a cross-sectional view a second example of a solder
pad 10. The solder pad 10 may have the surface 12 on which the tin
layer 14 may be arranged. On top of the tin layer 14 a bismuth
layer 18 may be arranged. On top of the bismuth layer 18 an
antimony layer 20 may be arranged. On top of the antimony layer 20
a nickel layer 22 may be arranged. Although not visible in FIG. 2,
each layer may cover essentially the entire respective underlying
layer. The thickness of the tin layer 14 may be the same as
explained with reference to FIG. 1.
The thickness of the bismuth layer 18 may lie in a range from about
2 micrometer to about 10 micrometer. In one example, the thickness
of the bismuth layer 18 may lie in a range from about 4 micrometer
to about 8 micrometer. In a further example, the thickness of
bismuth layer 18 may lie in a range from about 5 micrometer to
about 7 micrometer.
The antimony layer 20 may have a thickness which may lie in a range
from about 1 micrometer to about 6 micrometer. In one example, the
thickness of antimony layer 20 may lie in a range from about 2
micrometer to about 5 micrometer. In another example, the thickness
of antimony layer 20 may lie in a range from about 3 micrometer to
about 4 micrometer.
The nickel layer 22 may have a thickness that may lie in a range
from about 0.1 micrometer to about 0.6 micrometer. In one example,
the thickness may lie in a range from about 0.2 micrometer to about
0.5 micrometer. In a further example, the thickness of nickel layer
22 may lie in a range from about 0.3 micrometer to about 0.4
micrometer.
A relation of a thickness of the bismuth layer 18 to a thickness of
the nickel layer 22 may be about 20:1. A relation of a thickness of
the bismuth layer 18 to a thickness of the antimony layer 20 may be
about 2:1. A relation of a thickness of the antimony layer 20 to a
thickness of the nickel layer 22 may be about 10:1. A relation of a
thickness of the tin layer 14 to a total thickness of the bismuth
layer 18, the antimony layer 20 and the nickel layer 22 may be
between about 0.3:1 and 5:1.
FIG. 2 shows a layer stack including on top of the tin layer 14,
first the bismuth layer 18, then the antimony layer 20 and then the
nickel layer 22. It is to be understood that an order of the three
layers (bismuth, antimony and nickel) may be different. For
example, the antimony layer 20 may be deposited directly on the tin
layer 14 followed by the bismuth layer 18.
As for the first example shown in FIG. 1, an interaction will take
place when soldering the solder pad 10 with its surface 12
including the overlying layers 14, 18, 20 and 22 with a standard
SAC387 to a board. Solder SAC387 may form an alloy with the
materials tin, bismuth, antimony and nickel which may improve
stability of the solder joint especially during temperature
cycles.
FIG. 3 shows a third example of an enhanced solder pad 10 having
the surface 12. In the third example, the solder pad 10 may have on
its surface 12 the same layer stack as shown in FIG. 2, beginning
with a tin layer 14A, a bismuth layer 18A, an antimony layer 20A
and a nickel layer 22A. In contrast to the second example, the
third example is a multi-stack example. In other words, on top of
the nickel layer 22A a new layer stack may start with a tin layer
14B arranged on top of the nickel layer 22A. A bismuth layer 18B
may be arranged on the tin layer 14B. An antimony layer 20B may be
arranged on the bismuth layer 18B. A nickel layer 22B may be
arranged on the antimony layer 22B. The layers 14B, 18B, 20B and
22B may form a second layer stack. On top of the second layer
stack, a third layer stack may be formed. On top of the nickel
layer 22B a tin layer 14C may be arranged. On top of the tin layer
14C a bismuth layer 18C may be arranged. On top of the bismuth
layer 18C an antimony layer 20C may be arranged. On top of the
antimony layer 20C a nickel layer 22C may be arranged. The third
example, as shown in FIG. 3, is a three layer stack example. It is
understood that instead of three stacks also two, four or another
number of superposed stacks is possible.
The three stacks shown in FIG. 3 are illustrated as being of a
greater total thickness compared to the stack of FIG. 2. It is
understood that this may not be necessarily true in a real
application. The thickness of the tin layer 14A plus the thickness
of the tin layer 14B added to the thickness of the tin layer 14C
may lie in a range from about 5 micrometer to about 15 micrometer.
For example, each of the three tin layers may have a thickness of
about 2 micrometer, summing up to a total thickness of 6
micrometer. In another example, each of the tin layers 14A, 14B and
14C may have a thickness of about 5 micrometer adding up to about
15 micrometer. The tin layers 14A, 14B and 14C are not necessarily
of the same thickness. Each of the tin layers 14A, 14B and 14C may
have another thickness. In an example, the thickness of the tin
layer 14A may be about 3 micrometer. The thickness of the tin layer
14B may be of about 2 micrometer. The thickness of tin layer 14C
may be of about 1 micrometer. The total thickness of the tin layers
14A, 14B and 14C may then be about 6 micrometer and may lie in a
range from about 5 micrometer to about 15 micrometer. In a further
example, the total thickness of the tin layers 14A, 14B and 14C may
lie in a range from about 7 micrometer to about 12 micrometer. In
another example, the total thickness of the tin layers 14A, 14B and
14C may lie in a range from about 9 micrometer to about 11
micrometer.
The same holds true for the bismuth layers 18A, 18B and 18C, the
antimony layers 20A, 20B and 20C and the nickel layers 22A, 22B and
22C which may be of equal thickness or different thicknesses with a
range of a total thickness for each material as given below.
The total thickness of the bismuth layers 18A, 18B and 18C may lie
in a range from about 2 micrometer to about 10 micrometer, or from
about 4 micrometer to about 8 micrometer.
In a further example, the total thickness of the three bismuth
layers may lie in a range from about 5 micrometer to about 7
micrometer. It is understood that in an example including more than
three stacks or less than three stacks, the range of total
thickness does not necessarily vary. Only the thickness per layer
is changed. Again the bismuth layers 18A, 18B and 18C are not
necessarily of the same thickness. In an example, the bismuth layer
18A may have a thickness of 3 micrometer, the thickness of the
bismuth layer 18B may be of 1 micrometer and the thickness of the
bismuth layer 18C may be of 3 micrometer giving a total thickness
of 7 micrometer which lies in a range from about 2 micrometer to
about 10 micrometer. The thicknesses of the bismuth layers 18A, 18B
and 18C may be also the same, for example, each one micrometer.
The total thickness of all antimony layers 20A, 20B and 20C may lie
in a range from about 1 micrometer to about 6 micrometer. In one
example, the thickness may lie in a range from about 2 micrometer
to about 5 micrometer. In another example, the total thickness of
all antimony layers may lie in a range from about 3 micrometer to
about 4 micrometer.
A total thickness of the nickel layers 20A, 20B and 20C may lie in
a range from about 0.1 micrometer to about 0.6 micrometer. In one
example, the total thickness of the nickel layers 20A, 20B and 20C
may lie in a range from about 0.2 micrometer to about 0.5
micrometer. In a further example, the total thickness of the nickel
layers may lie in a range from about 0.3 micrometer to about 0.4
micrometer.
In the multi-stack layer example of FIG. 3 forming of an alloy
while soldering the solder pad using an SAC387 solder may be
further enhanced due to the alternating layers. The sequence or
order of the layers is not necessarily the same in all stacks.
FIG. 4 shows a fourth example of a solder pad 10 with a surface 12.
On the surface 12 a tin layer 24 may be arranged. The tin layer 24
may be applied as a reflowed metal particle paste. The tin layer 24
may include particles of at least one out of bismuth particles,
antimony particles and nickel particles. During a soldering process
the tin may melt and the particles 26 and the tin may interact with
the solder components of SAC 387 to form a resistant solder
joint.
FIG. 5 shows a fifth example of a solder pad 10 with surface 12. On
the surface 12 a tin layer 28 may be arranged. The tin layer 28 may
be applied as a reflowed metal particle paste. The tin layer 28 may
include bismuth particles 30, antimony particles 32 and nickel
particles 34. In the example of FIG. 5, the bismuth particles are
schematically illustrated as empty circles. In addition, the
antimony particles are schematically illustrated as black points or
filled circles. Further, the nickel particles are schematically
illustrated as crossed circles. In an example, the effective volume
percentage of tin in the tin layer 28 may lie in a range from about
20% to about 60%, or from about 30% to 50%.
In an example, the effective volume percentage of bismuth particles
30 in tin layer 28 may lie in a range from about 10% to about 40%.
In a further example, the effective volume percentage of bismuth
may lie in a range from about 20% to about 30%.
In an example, the effective volume percentage of antimony
particles 32 in the tin layer 28 may lie in a range from about 5%
to about 20%. In a further example, the effective volume percentage
of antimony may lie in a range from about 10% to about 15%.
In an example, the effective volume percentage of nickel particles
34 in the tin layer 28 may lie in a range from about 1% to about
3%. In a further example, the effective volume percentage of nickel
in the tin layer 28 may lie in a range from about 1.5% to about
2.5%.
FIG. 6 schematically illustrates an electronic component 40 in a
cross-sectional view. The electronic component 40 may include a
leadframe 42. The leadframe 42 may have a die pad 42A and two lead
pads 42B. A chip or die 44 may be attached to a first surface of
the die pad 42A. Contacts of the die 44 (not illustrated) may be
electrically connected via bond wires 46 to the lead pads 42B. A
surface of the leadframe 42, which may form a solder pad surface
48, may be opposite to the surface on which the die 44 may be
attached. The solder pad surface 48 may be opposite to a surface of
the lead pads 42B to which the bond wires 46 may be connected
to.
The electronic component 40 may further include a mold compound 50
forming a package. The package or mold compound 50 may cover the
die 44, the bond wires 46 and at least partly the leadframe 42. The
solder pad surface 48 may be not covered by the mold compound 50
and may form a mounting surface. On the solder pad surface 48 a
layer 52 may be applied. It is understood that the layer 52 may
correspond to the tin layer 28, as shown in FIG. 5, or to the tin
layer 24, as shown in FIG. 4. In further examples, the layer 52 may
correspond to a layer stack or a plurality of layer stacks as
explained with reference to FIGS. 1 to 3. In other words, the layer
52 may include a tin layer 14, a bismuth layer 18, an antimony
layer 20 and a nickel layer 22. It is understood that the layer 52
may be applied onto the solder pad surface, once the electronic
component 40 is finished. In another example, the layer 52 may be
applied onto the leadframe before finishing the electronic
component.
In a further example, the electronic component may include a
so-called leadless package. A leadless package does not necessarily
include any leads extending from the package. A solder pad surface
may be provided on a mounting surface of the package. On the solder
pad surface a layer may be arranged which may correspond to the tin
layer 28, as shown in FIG. 5, to the tin layer 24, as shown in FIG.
4 or to a layer stack or a plurality of layer stacks as explained
with reference to FIGS. 1 to 3.
FIG. 7 schematically illustrates a method for enhancing a solder
pad surface. In a step S1, a solder pad with a solder pad surface
may be provided. In a step S2, tin may be plated or sputtered onto
the solder pad surface to form a tin layer. In a step S3, bismuth
may be plated or sputtered onto the tin layer to form a bismuth
layer. In a step S4, antimony may be plated or sputtered onto the
bismuth layer to form an antimony layer. In a step S5, nickel may
be plated or sputtered onto the antimony layer forming a nickel
layer. In a further example, steps S2 to S5 may be repeated one or
more times to form a multi-stack example as shown in FIG. 3.
The enhanced solder pad surface may allow reliable package
soldering onto a PCB with SAC solder paste. During the soldering
process a bulk material may be formed which may provide a reliable
solder joint.
It is understood that the proposed solder pads and enhancement of
solder pads are not limited to a mounting of electronic components
to boards. Rather, any solder joint may be improved by arranging
the above described layers on a solder pad surface.
While the examples have been illustrated and described with respect
to one or more implementations, alterations and/or modifications
may be made to the illustrated examples without departing from the
concept of the appended claims. In particular regard to the various
functions performed by the above described structures, the terms
(including a reference to a "means") used to describe such
structures are intended to correspond, unless otherwise indicated,
to any structure which performs the specified function of the
described structure (e.g., that is functionally equivalent), even
though not structurally equivalent to the disclosed structure which
performs the function in the herein illustrated exemplary
implementations of the disclosure.
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